Question

Tính hợp lí, nếu có thể

a) 45.18+18.53              b) ( 7/8+1/2):11/16               c) 1/6+1/12+1/20+1/30+......+1/90+1/110

Answer 1

a, có người giải ùi khỏi làm nữa

b, (7/8 + 1/2) : 11/16

= 7/8 : 11/16 + 1/2 : 11/16

= 14/11 + 8/11

= 2

c, \(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}+\frac{1}{110}\)

= \(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}+\frac{1}{10.11}\)

= \(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+..+\frac{1}{10}-\frac{1}{11}\)

= \(\frac{1}{2}-\frac{1}{11}\)

= \(\frac{9}{22}\)

Answer 2

2NHEBAN